1. Field of the Invention
This invention relates to recording materials, particularly thermographic and photothermographic image-recording materials employing certain di- and triarylmethane dye precursor compounds and to a method of forming color employing the dye precursor compounds.
2. Background Art
Various dry image-recording materials that can be processed by a dry method only, that is, without the use of any treatment with liquids have been proposed. Among such image-recording materials are the thermographic and photothermographic materials of the silver salt type which employ moderate heating to develop a visible image and which comprise an oxidation-reduction image-forming combination comprising a non-photosensitive organic silver salt oxidizing agent such as the silver salt of a long chain fatty acid and a reducing agent for silver ions, typically, an organic reducing agent. In addition to the above, the photothermographic materials also include a photosensitive compound such as a light-sensitive silver halide or a photosensitive compound-forming component such as a component capable of forming a light-sensitive silver halide. The latter materials are often referred to as heat developable photographic materials and require an imagewise exposure to light to form a latent image prior to the heat development step.
The addition of dye-forming compounds to materials of the silver salt type for providing a color image or a color enhanced image also has been proposed. Usually color formation is achieved by color coupling to form a dye image, for example, by including a color-forming coupler and using a p-phenylenediamine, sulfonamidophenol or other color-developing agent as the organic reducing agent or by oxidation of a leuco dye to its colored form, for example, by employing a readily oxidizable indoaniline or phenolic leuco dye as the organic reducing agent. These and other means for generating dye images in silver salt materials have been described by J. W. Carpenter and P. W. Lauf in their review of "Photothermographic Silver Halide Systems", Research Disclosure, No. 17029, June, 1978. The formation of multicolor images using at least 2 or 3 color image-forming layers also has been disclosed in U.S. Pat. Nos. 4,021,240, 4,452,883 and 4,460,681.
Other dry image-recording materials for producing color images from colorless precursor(s) also have been proposed. One system commonly employed for pressure-sensitive and heat-sensitive recording materials to produce dye images comprises a two-component system utilizing a coloration reaction between a colorless dye precursor (color former) and an acidic material (color developer). Among the colorless dye precursors used as the color former are triarylmethane compounds including bridged triarylmethane compounds possessing a lactone, lactam or other ring-closing moiety, for example, 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (Crystal Violet Lactone), 3-piperidino-6-methyl-7-anilinofluoran and Rhodamine B anilinolactam. The acidic material used as the color developer is usually a phenol derivative or an aromatic carboxylic acid derivative, for example, p-tert-butylphenol, 2,2-bis(p-hydroxyphenyl) propane, o-hydroxy-naphthoic acid, p-hydroxybenzoic acid, 3,5-di-tert-butylsalicylic acid and so forth.
In these two-component systems, the color former and the color developer can be carried on the same or on separate supports. Where the two components are coated on the same side of a common support, a binder or some other means such as encapsulation is employed for physically separating the color former and color developer to prevent premature mixing and coloration. Images are formed by the imagewise application of pressure, heat, electricity or other stimulus to effect contact between the two components to bring about the coloration reaction. Depending upon the dye precursor used as the color former, the coloration reaction brought about by contacting the two components may comprise dissociation, or it may comprise ring-opening in those compounds containing a cyclic ring-closing moiety as part of their structure. For example, color formers such as the aforementioned triarylmethane compounds possessing a lactone or lactam moiety ring-closed on the methane carbon atom become ring-opened and colored by an ionization or hydrogen-bonding reaction when contacted with the acidic material. Such imaging systems for pressure-sensitive, heat-sensitive and electrothermic recording materials are described in U.S. Pat. Nos. 3,924,027, 4,502,067, 4,133,933 and in U.S. Pat. No. 4,132,436.
Although 3,3-disubstituted thiophthalides and dithiophthalides have been disclosed previously, none of the triarylmethane compounds described are dye precursors, i.e., color formers, since they do not exhibit the color-forming properties of dyes. In particular, R. Meyer, Ber. 33, pp. 2570-2576 and R. Meyer and J. Szanecki, ibid, pp. 2577-2583 disclose the synthesis of 3.3-dithiotluorane, dithiophenylphthalide (3,3-diphenylthiophthalide) and dithiodichlorofluorane by fusing the corresponding phthalides with phosphorus pentasulfide. The 3.3-dithiofluorane and the dithiodiphenylphthalide lack the auxochromic substituents necessary to complete the auxochromophoric system of a triarylmethane dye. The dithiodichlorofluorane also does not exhibit the properties of a dye, presumably because the chloro groups are not providing an auxochromic effect.
I. P. Soloveichik, et al., Zhurnal Organicheskoi Khimii, Vol. 10, No. 3, pp. 615-618, March, 1974 disclose the preparation of 3,3-diphenylthiophthalide by reacting the 3,3-diphenyldithiophthalide of Meyer and Szanecki with mercuric acetate and also by reacting o-benzoylbenzoic acid and phosphorus pentasulfide followed by phenylation with the Friedel-Crafts reaction as previously described by I. O'Brochta, et al., J. Am. Chem. Soc., 61, 2762 (1959). U.S. Pat. No. 2,097,435 discloses a synthesis for thiophthalides including 3,3-diphenylthiophthalide by reacting the corresponding phthalide with sodium hydrosulfide under anhydrous conditions in the absence of air or oxygen. Like the 3,3-diphenyldithiophthalide discussed above, 3,3-diphenylthiophthalide is not a dye precursor since the 3,3-phenyl moieties lack an auxochromic substituent to impart dye properties.
As discussed in Gilman, Henry, Organic Chemistry, An Advanced Treatise, Vol. III, John Wiley & Sons, New York, 1953, pp. 247-55, a chromophore called a chromogene may be colored but does not yet represent a dye. To achieve this a further introduction of salt-forming groups, "auxochromes", into the molecule is required. The function of chromophore and auxochrome groups according to modern theory is necessary for modifying the molecule so as to introduce the possibility of resonance and thus color.